1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display and a scanning backlight driving method of the liquid crystal display.
2. Discussion of the Related Art
A range of application for liquid crystal displays has gradually widened because of its excellent characteristics such as light weight, thin profile, and low power consumption. The liquid crystal displays have been used in personal computers such as notebook PCs, office automation equipments, audio/video equipments, interior/outdoor advertising display devices, and the like. A backlit liquid crystal display occupying most of the liquid crystal displays controls an electric field applied to a liquid crystal layer and modulates light coming from a backlight unit, thereby displaying an image.
When a liquid crystal display displays a motion picture, a motion blur resulting in an unclear and blurry screen may appear because of the characteristics of liquid crystals. The motion blur may appear in the motion picture, and the motion picture response time (MPRT) has to be reduced so as to remove the motion blur. A related art scanning backlight driving technology was proposed so as to reduce the MPRT. As shown in FIG. 1, the scanning backlight driving technology provides an effect similar to an impulsive drive of a cathode ray tube by sequentially turning on and off a plurality of light sources Lamp 1 to Lamp n of a backlight unit along a scanning direction of display lines of a liquid crystal display panel, thereby solving the motion blur of the liquid crystal display.
However, the related art scanning backlight driving technology was applied to only the LCD models with 120 Hz or more and was not applied to the 60 Hz LCD models. This is because a user easily perceived 60 Hz flicker when the related art scanning backlight driving technology was applied to the 60 Hz LCD model as shown in FIG. 2.
Further, because the related art scanning backlight driving technology turns off the light sources of the backlight unit for a predetermined time in each frame period, the screen becomes dark. As a solution thereto, a method for controlling the turn-off time of the light sources depending on the brightness of the screen may be considered. However, in this instance, the improvement effect of the motion blur of the related art scanning backlight driving technology is reduced because the turn-off time is shortened or omitted in the bright screen.
A liquid crystal display includes a liquid crystal display panel configured to display modulated data based on a frame frequency, light sources configured to generate light to be irradiated into the liquid crystal display panel, a scanning backlight controller configured to calculate a turn-on duty ratio of a pulse width modulation (PWM) signal for controlling turn-on and turn-off operations of the light sources, and a light source driver configured to synchronize a frequency of the PWM signal with the frame frequency or with a frequency, that is faster than two times the frame frequency, based on the result of a comparison between the turn-on duty ratio of the PWM signal and a previously determined critical value and then sequentially drive the light sources along a data scanning direction of the liquid crystal display panel.
In another aspect, there is a scanning backlight driving method of a liquid crystal display including a liquid crystal display panel and light sources generating light to be irradiated into the liquid crystal display panel, the scanning backlight driving method including calculating a turn-on duty ratio of a pulse width modulation (PWM) signal for controlling turn-on and turn-off operations of the light sources, and synchronizing a frequency of the PWM signal with a frame frequency for displaying modulated data on the liquid crystal display panel or with a frequency, that is faster than two times the frame frequency, based on the result of a comparison between the turn-on duty ratio of the PWM signal and a previously determined critical value, and then sequentially driving the light sources along a data scanning direction of the liquid crystal display panel.